Animal Diversity Web

Ants are placed in a single family, the Formicidae. They belong to the order Hymenoptera, which includes bees, wasps, sawflies, and ichneumons.

A characteristic of most formicids is the possession of a metapleural gland. This gland produces phenylacetic acid, which fights against fungi and bacteria. It is made up of a pair of cell clusters which lead to two chambers in the rear of the ant's middle body. While the gland is the most diagnostic trait separating ants from other Hymenoptera, it is not universal among ants. Many arboreal species lack the metapleural gland (due perhaps to the drier, cleaner environment). Another trait that characterizes ants is their body structure. The ant head is connected by a thin neck to the thorax, which is then connected by a thin "waist" to the abdomen. While this is the general structure of many insects, ants are distinguished by the waist, which is pinched down posteriorly at its connection with the abdomen.

Native ants can be found everywhere in the world, excluding Antarctica, Iceland, Greenland, parts of Polynesia, and a few remote islands in the Atlantic and Indian Oceans. Within this vast range, 8,800 species have been documented, although upwards of 20,000 species have been estimated to exist. An exact figure would be exceedingly difficult to determine, since many species are difficult to differentiate. Ants can live in nearly every terrestrial habitat and environment, including deserts, beaches, in walls, and abandoned plumbing. Some species have even been known to survive underwater for as long as fourteen days by going into an anesthetized state, in which oxygen intake decreases to twenty times below the need of the ant when asleep.

Ants have a highly structured social system, a feature which has developed in only a few insects, including termites, bees, and wasps. Two or more generations coexist, with the adult ants caring for the young. Ants are divided into castes, with reproductive queens and kings, and sterile workers (all of which are female). Ant colonies vary greatly in their social structure, but three basic stages in the development and life of a colony exist. The first of these is the founding stage, in which a young virgin queen (female alate) leaves the nest of her mother. She flies until she has met and been inseminated by a few males. The males soon die without returning to their nests. Then the female finds a suitable place in the soil or in a rotting tree to build her nest. She forages and cares for her first brood until they are adults. Next the colony enters the second stage, known as the ergonomic stage. Now the queen devotes herself to egg-laying while the workers forage, care for the young, and enlarge the nest. This stage, which centers on colony growth lasts for a period ranging from four months to five years, depending on the species of ant. When the colony is a suitable size, it finally enters into the last stage, the reproductive stage. Now new queens and males are produced, which later leave the nest to produce new colonies, beginning the cycle again.

Ants exemplify many behaviors and phenomena which are common to other insect species. For this reason, studies have been done on topics including:

• Kin selection
• Competition among individuals of the same colony, of different colonies, and of different species
• Hierarchy in control processes
• The nature of behavioral regulatory processes in social organization.
• The shaping of castes by natural selection to contribute to the genetic fitness of the colony as a whole
• The effects of competition on community structure

Ants are of extreme importance in the insect world. They have complex and often obligatory relationships with various plants, which depend on the ants for their wellbeing. These include seed dispersal, pollination, defense by ants against attacks by herbivores, and enrichment of soil through soil turning. Ants also contribute substantially to the enormous biodiversity of insects, and their richly complex lives and relationships have provided scientists with numerous insights concerning evolutionary and ecological phenomena.

A large number of ants have been perfectly preserved in amber. By observing this clear fossil record, much can be found out about ant evolution, such as the evolution of ants from a primitive form of wasp. That species, Sphecomyrma, appears to be the link between modern ants and primitive wasps. Sphecomyma was the first known species to posses the metapleural gland, a key ant characteristic.

Reference:

Holldobler and Wilson. The Ants. Belknap Press of Harvard University Press, Cambridge, Mass., 1990.

Contributors

Jennifer Roof (author), University of Michigan-Ann Arbor.